Video Transcript
Kilograms
In this video, we’re going to learn
how to use kilogram weights and a scale to measure the mass of objects. A kilogram is a unit of measurement
that we use for measuring mass. You may come across people using
the word kilo. This is just a shorter way of
saying kilogram. Also, we often use the letters kg
to represent kilograms. Saves us writing out the word all
the time. Now, what does a kilogram look
like? You may’ve seen something like this
before. It’s a kilogram weight. It’s made out of metal and it
weighs exactly one kilogram. We can use weights like this to
help measure the mass of objects.
Do you have an idea how much this
would weigh if you picked it up? It’s often useful to have an idea
of objects that weigh around about one kilogram. This can help us to visualize or
imagine how heavy a kilogram is. Can you imagine picking up a
pineapple? This weighs about the same as a
kilogram. The sort of bags of rice that you
might find in a kitchen cupboard often weigh a kilogram.
It’s also about the same mass as
one of those large dictionaries that you can get. You can also get some small laptops
that weigh one kilogram too. And here’s a really interesting
fact. If we don’t count the bottle, a
liter of water weighs exactly the same as one kilogram. Perhaps you have your own way of
remembering how heavy one kilogram is. But hopefully these objects may
help you.
When we look at the word kilogram,
we can see that part of it is the word gram. We can measure the mass of objects
using grams too. It’s another unit of
measurement. But the kilogram is a heavier unit
than grams are for measuring mass. We often measure the mass of more
heavy objects in kilograms. So how can we use kilograms to find
the mass of objects? Well, there’re two ways really. The first is using what we might
call a set of balances or weighing scales. The word balances is interesting
here, though, because we need to look at our scales and think about how they are
balanced.
At the moment, the two ends of our
scale are balanced. There’s nothing on them. They both weigh the same. Oh dear, what’s about to happen
now? Our scales aren’t balanced
anymore. This is because the bird is heavier
than what’s on this end. There’s nothing on this end, is
there? Let’s put a kilogram weight on the
other end and see what happens. This is interesting. The scales still unbalance, but
this time, they’ve changed direction. What can we say about the mass of
the bird? We don’t know exactly how heavy it
is. But what we do know is that the
bird is lighter than a kilogram.
We can tell this because of what’s
happened to the set of balances. Let’s take the kilogram weight off
for a moment. Oh dear, here we go. Oh this is getting silly. Let’s find out the mass of these
three birds before they fall off. The birds are heavier than one
kilogram. The scales are now balanced. This time we can say exactly how
heavy the birds are. These birds weigh two
kilograms.
Now there’s another piece of
equipment that we can also use to measure mass in kilograms. These are a set of weighing
scales. Can you see there’s a dial on the
front of them? This part of the scales is where
we’re going to read how heavy things are. If you know how to read a number
line like this, you can easily read these scales because the dial on the front is
just a curved number line. And on these scales, we can see the
numbers from one to nine. And if we look carefully, we can
see that the unit of measurement is kilograms.
At the moment, the arrow is
pointing to zero because nothing is on the scales. So all we need is something to
weigh. Let’s weigh this cactus. We just need to put it on the
scales. If we look at where the arrows move
to, we can see that it’s halfway between the numbers three and four. We can say that the cactus weighs
three and a half kilograms. We found out the weight by reading
the scales. Let’s have a go now at answering
some questions where we have to use kilogram weights and a scale to measure the mass
of some objects.
Are the bananas heavier or lighter
than a kilogram?
In the picture, we can see a set of
balancing scales. On one end, there’s a bunch of
bananas. And at the other end, we have a
metal weight. We can see that this is labeled one
kg. And this shows us that the unit of
measurement is a kilogram. This is a kilogram weight. So what these scales are helping us
to do is to compare the masses of these two objects. And this is why the question asks
us, are the bananas heavier or lighter than a kilogram?
What do you notice about the
position of the scales? This end of the scales is further
down, isn’t it? This shows that the kilogram weight
is heavier than the bananas. So we can say that the bananas are
lighter than the kilogram. We don’t know how heavy the bananas
are exactly. But by looking at our set of
balances, we can say that the bananas are lighter than a kilogram.
Fill in the blank: The mass of the
puppy is what kilograms.
In the picture, we can see a set of
balancing scales. This is the sort of equipment we
can use to help weigh the mass of different objects. In this case, we’re using them to
measure the mass of a puppy. And we can see the puppy at one end
of our measuring scales. And at the other end, we have what
look like some metal weights. Can you see what’s written on
them? Each of the weights is labeled one
kg or kilogram. So how many kilograms are at this
end of our scales? There are four of them. Each one is worth one kilogram, so
we can say that there are four kilograms altogether.
Now our question asks us to fill in
the blank with the mass of the puppy. In other words, how heavy does the
puppy weigh? Well, we could just look at our
kilogram weights and say it weighs four kilograms. And that it’s actually the right
answer. But before we say that, we need to
think carefully. Why is the mass of the puppy four
kilograms? And it’s not just because four
kilograms are on the other end of our scales.
These scales have four kilograms at
one end and a puppy at the other. But on these scales, the puppy is
lower than the four kilograms. If our scales look like this, we
would know that the puppy was heavier than four kilograms. It would weigh more than four
kilograms. And if our set of scales look like
this, again, we’d still have four kilograms on one end and a puppy on the other. But this time, it’s the four
kilogram weights that’re heavier. This end of our set of scales is
pushed down. The puppy is lighter than four
kilograms. And so in this example, we would
say that the puppy is less than four kilograms.
Now, let’s come back to our
picture. How would you say we know that the
mass of the puppy is four kilograms? Yes, there are four kilograms at
one end and a puppy at the other. But the important thing is that our
scales are balanced; both ends of the scale weigh the same. The mass of the puppy is equal to
four kilograms. Can you see how they’re both level
with each other? We didn’t just find the answer by
counting the number of kilograms. We looked at the fact that our
weighing scales were balanced. And we know now that the mass of
the puppy is four kilograms.
Emma weighed a pumpkin and a
watermelon. Figure out the mass of the
pumpkin.
This is a really interesting
question. We need to figure out or work out
the mass of a pumpkin. And we’re given some pictures to
help us. The only trouble is none of the
pictures show that Emma has weighed a pumpkin on its own. She’s used this set of balancing
scales to weigh a pumpkin and a watermelon together. And then, she’s just used a
different set of scales to weigh the mass of a watermelon on its own. We need to use these two pieces of
information to work out the mass of what the pumpkin weighs on its own.
First of all, let’s look at the
pictures and work out what each set of scales is showing. Once we’ve done that, we can think
about how we can work out the answer. Before we start, let’s make sure
that we’re measuring in the same unit of measurement. Can you see the letters kg on both
sets of scales? We know that kg is short for
kilograms. And kilograms are a unit of
measurement that we can use to measure the mass of heavier objects like pumpkins or
watermelons.
Let’s look at our first set of
scales. To begin with, we can see that
they’re balanced. In other words, one end isn’t
heavier than the other. They both weigh the same. It’s like being on a seesaw where
someone on the other end is exactly the same mass as you. So we can use this set of scales to
work out how heavy a pumpkin and a watermelon together are. Let’s count how many kilograms
there are. We can see three weights on the
bottom and two on the top. So that’s five kilogram weights
altogether. The pumpkin and the watermelon
weigh five kilograms together.
Now let’s read our second set of
scales. These have got a dial on the front
of them. And there’s a needle that
moves. Can you see which number it’s
pointing to? By putting the watermelon on these
scales, it’s made the needle point to the number two. So we now know how heavy the
watermelon is on its own. It’s two kilograms. Now, it’s time to use these two
pieces of information to help work out the answer. Let’s use a part–whole model to
help us.
We know that the total mass of a
pumpkin and a watermelon is five kilograms. And we also know that the mass of a
watermelon on its own is two kilograms. Can you see how we can work out the
answer? We just need to think what goes
with two to make five. We know that five take away two
equals three. We didn’t need to weigh the pumpkin
on its own. We used the information on both
sets of scales to help us. The mass of a pumpkin on its own is
three kilograms.
What have we learned in this
video? We’ve been introduced to the
kilogram and some objects that weight about the same as a kilogram. We’ve also learned how to use
kilogram weights and a scale to measure the mass of objects.
